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Controlling a Hobby Servo using an AVR Microcontroller

We will control a hobby servo using an AVR microcontroller by outputting a PWM (Pulse Width Modulation) signal from the microcontroller to the servo. We will be using much of the information from the previous video and information on the fundamentals of PWM. We will also learn some new jargon that is specific to the AVR microcontrollers.

First, we will need to select a timer and the correct WGM (Waveform Generation Mode) within this timer that will be appropraite for the servo. Next, we need to select the PWM period that will work with the servo. The servo used in the video accepts a period 20 miliseconds long and we will take advantage of the ICR1 register to create this period. To do this, we will need to determine a prescaler so the timer uses the microcontroller's clock source properly, we will need to set the PWM to be in the correct mode, inverted or non-inverted, where the pulse happens at the beginning of the period, or at the end of the period and finally, we will need to derermine which OCR (Output Capture Register) we will use, 1A or 1B. Read on...

Introduction to PWM for the AVR (Atmel) Microcontrollers

PWM stands for Pulse Width Modulation and is the method to produce variable voltages using digital means. Typically, variable voltages come from analog circuits, and digital circuits produce only two voltages, the high (5v, 3.3v, 1.8v, etc.) or low (0v). So how it is possible that digital circuits can produce avoltage that is between the high and the low voltages? If you bring a digital signal up and down, in a consistent manner, you will get a proportion of the voltage between the high and low voltage. Imagine if a digital signal was pulsed high (5v) and low (0v) evenly, say the signal was in the high state for 1 microsecond and in the low state for 1 microsecond, add a capacitor to smooth the signal, the voltage would measure 2.5 volts. Now, change the high voltage in the high state for 9 microseconds and in the low state for 1 microseconds, the voltage would measure 90% of 5 volts, or 5v x .9 = 4.5 volts. The 90% is significant because the duty cycle is represented as a percentage (%). The applications associated with PWM could be: thecontrol of motors, sound output, dimming LEDs, and producing approximated analog waveforms. Read on...

Joe Z.'s Unique Hello World Project

Image of joes hello world morse code LED microcontroller project

Everyone knows the first program is called the "Hello World" project. The Hello World program is intended for the newbie programmer get their feet wet and be as simple as possible. This is why, in the embedded realm, the Hello World programs is to simply turn on an LED. Joe didn't want to settle for the typical Light up, or blink the LED. He wanted to literally make a single LED communicate. How would a single LED communicate? Using morse code, obviously.

Making a Library for the Button

Image of a push button switch on a breadboard.

The button code with the accompanying software debouncing is a lot to put into a main routine. It's best that these sorts of code become tucked away in a library and re-used in all of the programs that you will be implementing puch buttons in your circuits. The new library that we put together include features of using multiple button switches and varying the debouncing threshold.

UART One-Way Communication (Chip-to-Chip)

breadboard circuit of the one-way UART communication circuit between two microcontrollers

If you need to control a a microcontroller from another microcontroller, this is a good way to do it. Use the UART (Universal Asynchronous Receiver/Transmitter) to communicate to another microcontroller with only one wire for the communications link.

UART Datasheet in Plain English

The USART Block diagram for the AVR Atmega

Are you the victim of not understanding the engineering esoteric language used in datasheets? Check out my version of the UART portion of the datasheet in plain english. I also try to add a few analogies to make the understanding of the UART a bit easier. I cover most of the main points that you need to get a good understanding. Moreover, all of the initializing and functions are shown in code format, rather than in a table format.

Intro to Servos

The full explanation and narrative of the introduction to servos and understanding of torque is being added.

Additions to the List of Future Tutorials

From an email request, I have added three new tutorials to the list: From Breadboard to PCB Prototype, Using a CNC Machine to create the PCB and Using Transistors with Microcontrollers.

Microcontrollers: A Beginner's Guide (Video Series)

Image of the Atmega32 microcontroller.Similar to the video series that I produced on how to build a CNC machine from the ground up (published at, I will be producing a similar set of videos on the use of the Atmel AVR Atmega32 Microcontroller. The video serieswill start as an introduction, but will then switch rapidly to example-based projects for the microcontroller.

I have been enthralled with microcontrollers and robotics, and have embarked on a specific endeavor to create a bipedal robot balancing on point feet--that is, balancing in all directions without falling. This has yet to be accomplished, but has been tried many times over. There is one exception (PETMAN from Boston Dynamics)that has been successful, using a human scale robot with human scale feet. The really cool thing with the PETMAN is that they have achieved great locomotion with a human-like walking gait.

So, as I wander towards my endeavor, I will be explaining the process from scratch on the use, programming and construction of circuits fusing the AVR Atmega32 microcontroller; hopefully overcoming many challenges along the way.

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If you find these video clips usefull, consider creating your own. They are searchable and very focused. It's a great way to get the fluff out!

Upcoming Tutorials:

SPI Communication (Chip to Chip)
Demonstration of the funtamental signal requirements and timings and then show examples of circuit and code to establish communication.
PID and Encoder Control for DC Motor (Servo Basics)
Explain the fundamentals of encoders and how encoders can determine position for a greater mechanical system. This typically requires PID (Proportional Integral Derivative) closed loop control and a thorough detailed explanation of this type of control will be investigated. Various encoder types will be examined along with various types of motors and mechanical advantage (gears, pulleys, chain, etc.). This will require some prerequisites in signal theory, which I will explain.
Introduction to Servos (video complete, official page soon to come)
I will do a run-down of the different types of servos out there and how they function. I will also get into the details of closed-loop control.
Servo Control Using the Standard PWM Output (video complete, official page soon to come)
PWM is the method used to control non-digital hobby servomechanisms. I will show how to simply control the servo using the 16-bit timer and the PWM channels.
Servo Control Using the Output Pins (video complete, official page coming soon)
PWM will still be the method to control the hobby servo, but we may want the microcontroller to drive more servos than the number of standard PWM channels will allow. Therefore we will investigate a method that uses standard pins as PWM output to control many servos.
Servo Control For Servos That Use Encoders
We will investigate the programming necessary to create a closed-loop system that reads an encoder and positions a motor to create an overall servomechanism.
Controlling High AC Voltage Devices Using Relays
Do you want to control a household device? Using a relay and a spare output pin on your microcontroller can do the trick. In this tutorial, we will control the stuff that would be plugged into the wall outlet.
Controlling Higher DC Voltage Devices Using Mosfets
Enough of this 5v limit. With Mosfets, you can send higher DC voltages to devices that would function better above the 5v limit that comes out of the microcontroller.
LED Control Using PWM
This tutorial is a precursor to motor control using PWM. We will control the brightness of an LED and make it fade in and out softly.
LCD 4-Bit Mode
Is your LCD taking up too many pins? In 4-bit mode, the LCD will only need 4 data lines--so your microcontroller can free-up 4 of the pins for other uses.
Introduction to Serial Communication
The basic fundamentals of serial communication will be explained in this tutorial.
Configuring and Communicating with the USART
Universal Synchronous Asynchronous Receiver Transmitter is the serial communication function in the microcontroller. We will communicate to and from the computer via RS-232 (with the help of the Max232 chip to adjust voltage levels), and we will also communicate with a digital servo with a single wire to serve as both TX (Transmit) and RX (Receive).
Motor Control Using PWM
This tutorial will delve into motor control. Using PWM, we will be able to increase and decrease the speed of a motor and even change motor direction.
From Breadboard to PCB Prototype
This tutorial will explain the process necessary to create a schematic in Cadsoft Eagle, layout the PCB (Printed Circuit Board) and build the prototype.
Using a CNC Machine to create the PCB
If you have access to a CNC Machine, PCB routing is a great way to create chemical free PCBs.
Using Transistors with Microcontrollers
Learn how to use transistors in your microcontroller projects.
Control of a Small Low-Current Stepping Motor
In this tutorial, a small low-current stepping motor will be controlled by the pins of the microcontroller.
Control of Higher Current and Higher Torque Stepping Motors
A larger stepping motor will be controlled using Mosfets and a separate higher voltage source; however the microcontroller will still be providing the control logic to these Mosfets.
Control of Stepping Motors Using A Driver
As an alternative to Mosfets, I will select various driver chips on the market today and use those to provide the high-powered driving current, again under the direction of the microcontroller.
Control of Stepping Motors Using the Translator/Driver Combination
This is where things get interesting with stepping motor control, since the microcontroller now becomes a processor for much broader control--with only the need to send out step pulses and a high/low signal for direction control.
Using Alternative Clocks
Alternative clocks such as crystals, RC circuits and others will be explained and connected to the microcontroller. We will use these devices to adjust the frequency of the microcontroller.
Interfacing a Shift Register to Expand the Number of Output Pins
Imagine what you could do with many output pins! Do I hear...LED array? We can also investigate using this device to communicate to the LCD with only a few wires.
Read a PIR Sensor
PIR (Passive Infra-Red) sensors will be explained and we learn to control these devices with the microcontroller.

Read an Ambient Light Sensor
We will connect an ambient light sensor to the microcontroller, and check its reading on the LCD.

Introduction to Interfacing with I2C
Inter-Integrated Circuit is a type of communication that is common with many sensors and devices. I will probably start with an accelerometer that communicates using this technology.
Read an IR Distance Sensor
An Infra-Red distance sensor will be connected to the microcontroller, and the information will then be displayed to the LCD.
UltraSonic distance Sensor Reading
An ultrasonic distance sensor will be connected to the microcontroller, and the distance displayed to the LCD.
Wireless Communication
I will do a survey of the wireless options that can be used with microcontroller and explain each of them.
Radio Frequency Wireless Communication
We will communicate with another device using wireless radio frequency communication.
Communication using Xbee and Zigbee Devices
We will investigate the use of Xbee and Zigbee products for wireless network communications.
GPS Interfacing
A GPS module will be interfaced to the microcontroller. The information will be parsed and delivered to the LCD. We may do some other interesting things with GPS as well.
Other Microcontrollers, such as the ARM and PIC will get tutorials of their own. When I begin with these tutorials, I will start another list.
Did I mess anything? Let me know!